This invention relates to thermoplastic compositions comprised of a blend of polymers. More particularly, it relates to a ternary polymer blend containing as one of the ingredients, a polyetherimide.
Polyetherimide resins are well known and are of considerable value for use in molding compositions because of their excellent physical, chemical and thermal properties. The high glass transition and heat deflection temperatures exhibited by these polymers permit their use in high performance applications previously reserved for metals and some thermoset resins. These high glass transition temperatures also require, however, that the polymers be processed at relatively high temperatures, compared to other injection moldable thermoplastics. High processing temperatures require more expensive equipment and greater energy costs. For many applications, it would be desirable to have a resin with a lower processing temperature, yet which maintains the toughness and other advantageous physical properties of polyetherimides.
It is known that the processing temperatures of polyetherimides can be reduced by forming blends of those polymers with polyesters, such as polyethylene terephthalate or polybutylene terephthalate. See, White et al., U.S. Pat. No. 4,141,927. Although such blends maintain many of the physical properties of polyetherimides, they have not been found to have the toughness or impact strengths characteristic of polyetherimides.
Binary blends of polyestercarbonate resins and polyetherimides have been prepared for the primary purpose of improving the thermal properties of the polyestercarbonates. See, Quinn et al., U.S. Pat. No. 4,430,484. Again, although these blends exhibit certain advantageous properties, they have not been found to possess the toughness or impact properties of polyetherimides.
Thus, there exists a need for a polymer blend which requires lower processing temperatures than polyetherimides, yet maintains the toughness and impact properties of those polymers.